diff options
authorGustavo A. R. Silva <gustavo@embeddedor.com>2019-06-06 19:46:17 -0500
committerGustavo A. R. Silva <gustavo@embeddedor.com>2019-07-25 20:13:54 -0500
commita035d552a93bb9ef6048733bb9f2a0dc857ff869 (patch)
parent2defb94edb44784b0b5064633e05c97fdb1b0e0f (diff)
Makefile: Globally enable fall-through warning
Now that all the fall-through warnings have been addressed in the kernel, enable the fall-through warning globally. Also, update the deprecated.rst file to include implicit fall-through as 'deprecated' so people can be pointed to a single location for justification. Cc: Masahiro Yamada <yamada.masahiro@socionext.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Michal Marek <michal.lkml@markovi.net> Cc: Kees Cook <keescook@chromium.org> Cc: linux-kbuild@vger.kernel.org Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2 files changed, 17 insertions, 0 deletions
diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst
index 49e0f64a3427..053b24a6dd38 100644
--- a/Documentation/process/deprecated.rst
+++ b/Documentation/process/deprecated.rst
@@ -119,3 +119,17 @@ array may exceed the remaining memory in the stack segment. This could
lead to a crash, possible overwriting sensitive contents at the end of the
stack (when built without `CONFIG_THREAD_INFO_IN_TASK=y`), or overwriting
memory adjacent to the stack (when built without `CONFIG_VMAP_STACK=y`)
+Implicit switch case fall-through
+The C language allows switch cases to "fall through" when
+a "break" statement is missing at the end of a case. This,
+however, introduces ambiguity in the code, as it's not always
+clear if the missing break is intentional or a bug. As there
+have been a long list of flaws `due to missing "break" statements
+<https://cwe.mitre.org/data/definitions/484.html>`_, we no longer allow
+"implicit fall-through". In order to identify an intentional fall-through
+case, we have adopted the marking used by static analyzers: a comment
+saying `/* Fall through */`. Once the C++17 `__attribute__((fallthrough))`
+is more widely handled by C compilers, static analyzers, and IDEs, we can
+switch to using that instead.
diff --git a/Makefile b/Makefile
index 9be5834073f8..bdf8eac51b07 100644
--- a/Makefile
+++ b/Makefile
@@ -843,6 +843,9 @@ NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
# warn about C99 declaration after statement
KBUILD_CFLAGS += -Wdeclaration-after-statement
+# Warn about unmarked fall-throughs in switch statement.
+KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough=3,)
# Variable Length Arrays (VLAs) should not be used anywhere in the kernel

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